Scorch and pre-crosslinking

Anyone please explain what is the difference between scorch and pre-crosslinking in LV Xlpe insulation!

Thanks

Hi brn,

"Scorching" is a term from rubber extrusion which of course long preceeded plastic extrusion. Generally, in rubber extruders, it referred to much the same unplanned crosslinking process as pre-crosslinking in XLPE although as I understand it, it was very closely associated with the shear heat generated by the extruder screw and to a lesser extent with the shear flow of the rubber through the breaker plate. Burning was also a possibility. In fact people often refer to some rubber compounds as being "very scorchy compounds".

The terms "pre-crosslinking" or "pre-curing" refer to XLPE or other XL plastics and although the process is still commonly associated with the heat generated by extruder screw shear or high melt temperatures, it is also associated with dead or slow plastic flow spots in the extruder and crosshead. These are the spots where crosslinking occurs as a longer time-temperature function.

The incorrectly crosslinked plastic is often referred to as "pre-cure".

We suggest you use the term "pre-crosslinking" or "pre-curing" when discussing XLPE or other XL plastic extrusion processes and curing problems. These terms refer to all voltages of XL plastics used as a dielectric or as a semiconducting layer. (LV, MV, HV and EHV).

This is my understanding but I am a mechanical engineer, not a chemical engineer, polymer engineer or polymer chemist.

Kindest regards,
Peter J. Stewart-Hay
Principal
Stewart-Hay Associates
www.Stewart-Hay.com